1. Field of the Invention
The present invention relates to an inverter circuit for use in, for example, an electronic oven comprising a semiconductor switching element for converting an electric power available from a commercial power outlet into a high frequency electric power, and a high voltage power source device for use in the electronic oven for boosting such high frequency electric power and for supplying it to a magnetron.
2. Description of the Prior Art
An electronic oven employing such a high voltage power source device as shown in FIG. 8 of the accompanying drawings is disclosed in, for example, the Japanese Laid-open Patent Publication No. 62-190692, published in 1987. The prior art high voltage power source device shown in FIG. 8 comprises a printed circuit board 1 having only one of the opposite surfaces formed with a patterned grounding conductor 2 to avoid any possible leakage of electric power between a high voltage circuit and a low voltage circuit. However, since the patterned grounding conductor 2 is formed only on one surface of the printed circuit board 1, the patterned grounding conductor 2 does not work on the leakage of electric power occurring on the opposite surface of the same printed circuit board 1. Also, since this electric power converting device is used in an electronic oven, and since the printed circuit board 1 may often been contaminated by vapor originating from food material being heated within the oven and/or moisture component and dust afloat in a kitchen, there is a relatively high possibility that the high voltage circuit and the low voltage circuit are electrically shortcircuitted through deposits of those contaminants.
As hereinabove discussed, even though the patterned grounding conductor 2 is formed on one surface of the printed circuit board 1, a deposit of contaminants such as, for example, water droplets and/or dust tends to constitute a cause for an unwanted leakage of electric power from the opposite surface to the surface of the printed circuit board 1 on which the grounding conductor 2 is formed and, therefore, the formation of the patterned grounding conductor 2 only on such surface of the printed circuit board 1 is ineffective to eliminate the occurrence of a leakage of electric power between the opposite surfaces of the printed circuit board 1.